Continuous Vacuum Drying of Whole Milk Foam

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Abstract
The principles developed on a batch scale for preparing vacuum foam-dried whole milk were successfully applied on a continuous basis. An integrated pilot plant and a nozzle that creates a foam in vacuum and distributes it as a thin layer onto the moving belt of a continuous vacuum dryer are described. Whole milk is concentrated under vacuum to a solid content (43% average) corresponding to a viscosity at 100 F of 32-43 centistokes. The concentrate is homogenized at 3000-500 psi and 135 F. Nitrogen is metered into the concentrate stream and a scraped-surface heat exchanger then simultaneously chills the concentrate to 35F and disperses the gas. Finally within a drying chamber maintained at reduced pressure, the gassed concentrate expands to a foam which is applied and dried on a continuous solid belt. The study was restricted to dryer chamber pressures (9 mm Hg and below) necessary to preserve the foam integrity during drying. The effects of process variables on dryer output and product quality are discussed. Reproducible operating conditions are given for preparing products of excellent quality.